Electrical conduction and thermodynamic properties of K2NiP2O7

The pyrophosphate K2NiP2O7 has been synthesized by the classic ceramic method and characterized by X-ray diffraction, solid-state P-31 magic angle spinning (MAS) NMR, and IR and electrical impedance spectroscopy. The solid-state P-31 MAS NMR, performed at 121.49 MHz, shows two isotropic resonances at -17.66 and -19.94 ppm, revealing the existence of two phosphorus environments in the structure. The electrical conductivity and dielectric properties have been investigated in the frequency and the temperature range of 200 Hz-1 MHz and 603-728 K, respectively. The frequency dependence of the conductivity is interpreted using the augmented Jonscher relation. The close values of activation energies obtained from the analysis of hopping frequency and dc conductivity imply that the transport is through ion hopping mechanism. The charge carrier concentration in the investigated sample has been evaluated using the Almond-West formalism and shown to be independent of temperature. Thermodynamic parameters such as the free energy of activation Delta F, the enthalpy Delta H, and the change in entropy Delta S have been calculated.